The present invention relates generally to a shutter for a camera having a motor for effecting opening and closing of a set of shutter sectors, and more particularly to a shutter for a camera in which the motor is decelerated during the opening movement of the sectors to accurately stop the sectors at desired positions.
In a shutter for a camera having a motor for rotating a rotor by conducting electricity to a coil to effect opening and closing of a shutter opening by sectors driven by the motor, the operation of opening the sectors is carried out by conducting electricity to the coil in a forward direction and the operation of closing the sectors is carried out by conducting electricity to the coil in a reverse direction, or by the return force of the rotor or by a return spring.
In such a shutter, the opening movement of the sectors is started by conducting electricity to the coil in the forward direction, and often the actual fully opened positions of the sectors differ from the desired positions due to the inertia of the moving parts, such as the rotor and the sectors. Hence, the applicants have proposed to store time data of exciting the coils in correspondence with respective exposure amounts based on characteristics of the shutter mechanism and to control the operation of opening and closing the shutter based on the stored time data (Japanese Patent Publication No. 7169/1995).
However, according to this method, the rotor undergoes accelerating motion by conducting electricity to the coil in the forward direction and accordingly, the sectors are fully opened rapidly in a short period of time and it is difficult to stop the sectors at the desired positions. Therefore, it has not been possible to construct, using this method, a program shutter which operates with high performance. Further, it is difficult to control the operational timings of the shutter such that flash light is emitted at a diaphragm aperture position in correspondence with a distance to an object to be photographed. Moreover, there exists a problem in that an error with respect to a proper value of the diaphragm aperture is increased by even a small deviation in the timing of the flashing light and excellent picture photographing cannot be carried out.
In order to resolve the above-described problems, according to an aspect of the present invention, during the opening movement of the shutter sectors by conducting electricity to the coil in the forward direction, electricity is periodically conducted to the coil in the reverse direction to decelerate the speed of the opening movement of the sectors. Thereby, the opening movement of the sectors is delayed as slow as possible and control of stopping the sectors at desired stop positions is facilitated. Further, control of flash timing is also facilitated and therefore, an inexpensive program shutter can be provided.
According to the invention, a shutter for a camera comprises sectors for opening and closing a shutter opening by reciprocal pivotal movement, a motor for reciprocally and pivotally moving the sectors by forwardly and reversely rotating a rotor by forward and reverse electricity conduction to a coil, a memory circuit stored with electricity conduction data of the coil in correspondence with operational characteristics of the motor and the sectors, and a control circuit for controlling electricity conduction to the coil in accordance with the brightness of an object to be photographed and executing exposure control in accordance with the brightness of the photographed object, wherein the electricity conduction data comprises pulses for rotating the rotor in a direction reverse to a direction of opening the sectors for reducing acceleration during the opening motion of the sectors and pulses for rotating the rotor in the direction of opening the sectors for continuing to open the sectors.